Diagnostic accuracy of resazurin based rapid test for Colistin susceptibility in Carbapenem resistant Acinetobacter baumanii isolated form ICU settings

Objective: To determine diagnostic accuracy of rapid resazurin based test for Colistin susceptibility testing in Carbapenem resistant Acinetobacter baumannii isolated from ICU patients. Study Design: Validation study. Place and Duration of Study: Department of Microbiology, Armed Forces Institute of Pathology, Rawalpindi Pakistan, from Jul to Dec 2022. Methodology: A resazurin based rapid test for Colistin susceptibility testing in Acinetobacter baumannii was assessed using a total of 100 clinical isolates from ICU patients. This test detects the presence of viable bacterial cells in Mueller-Hinton broth containing a predefined concentration of Colistin sulfate. Bacterial suspensions of the isolates are added to Colistin containing Mueller-Hinton broth on a 96-well polystyrene microtiter plate and incubated for 3 hours at 35° ± 2°C. Resazurin (a viability colorant) is then added to the wells and results are interpreted on basis of color change (from blue to pink in resistant isolates) after a total of 4 hours. Results: The test accurately detected resistance in all 12 resistant isolates and had a sensitivity and specificity of 100% and 97.7% respectively. False positive results were seen in 2 out of 88 sensitive isolates. The overall diagnostic accuracy of the test was 98%. Conclusion: This resazurin based test is in-expensive, easy to perform, accurate and provides earlier results in just 4 hours as compared to 16-24 hours with the routine lab methods. This test can serve as a good alternate to conventional methods in resource limited settings and for infection control purposes.